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Re: Getting Started with 3D Drawings.
Great work @pmorwale on getting your first 3D drawing set up! It is looking great.
As far as the 3D Export options. JSON is really the 3JS format and GLB is the binary version of glTF.
A possible workflow is to import the 3D Drawings representation into a CAD application to make getting started with creating an actual model quicker. This use case would make sense if you need a 3D model and only have 2D drawings.
We are also looking at the possibility of a future Revu update that would support importing one of these formats as a 3D PDF so that the 3D drawings could be marked up. This could be a powerful tool when creating an RFI to really illustrate the question being asked.
Do these workflows resonate with you? Can you think of any other use cases for having the exported 3D drawings?

Re: Getting Started with 3D Drawings.
@Peter Noyes Thanks for the information.
3D Drawings (3D PDFs) generated out of 2D Plans, Elevations & Sections will help a lot in Visualization, RFIs & Punch creations at Site.

Re: Layers that appear in the Layers section aren't in the markups section
For the first part of the question, the layers you're seeing in the PDF probably came from the authoring software (Autocad, Revit, etc..). The reason why they're not in the markups list is the markups themselves are not assigned to a layer.
For the rest of the post, the answer unfortunately is simply, not an option today.
Re: Spaces
Thank you this worked great. I did a Cut & Paste of the existing spaces into the new PDF however this was way faster and easier. Thanks again!

Re: True or False: You can add layers to a PDF that's already in a Studio Session.
Comment redacted as it no longer applies. Thanks @Marco M
Re: Studio session alert interface - group and sort by name or company
Ah yes - the group dialogue that requires me to manually enter email addresses instead of showing me the list of existing session members. I will try that.
My original request about being able to sort session members in the alerts dialogue still stands.
Thanks for the reply.
Re: Studio session alert interface - group and sort by name or company
You can certainly make groups for your alert distribution. Go into the Session Settings and the Permissions tab. Click the icon on the left that looks like a person outline with the gear icon. This lets you create a group named what you like and you can include any emails of those that should participate in that group.
Now when you go to the option to Alert Attendee for a markup, the groups will be at the top of the list.
Re: Roundup in Custom Columns
This is possible with a formula column. In this example, it is using the ceiling function on the Measurement property so that you have a new column that is the Measurement value rounded up.

Re: Structural Shape Tool Set Elevations and Sections
I love @Shanoc Halliday's solution and can see it used to solve a lot of common problems people face.
To build on it a little, I would make the "inner" lines a lighter shade of red to help distinguish them from the boundary lines. Plus, if you want to use the "change colors" option, then you can manage them separately.